Field of the Invention
The present invention relates generally to a variable valve timing arrangement for engines and more specifically to cam follower location in such an arrangement in order to vary valve events of intake and exhaust valves independently from one another.
Background
Internal combustion engines provide the power for the majority of modes of transportation here in the United States. In today's time, with dwindling fossil fuel supplies and environmental concerns, the emphasis placed on creating higher quality and more efficient engines has never been higher. In recent decades, there has been much emphasis placed on improving the control and operation of the valve train of an internal combustion engine due to its influence on the efficiency, emissions, power and overall performance of the engine. The primary reason that valve train has such significant effects on engine operation is that it primarily determines the volumetric efficiency of the engine. Volumetric efficiency is effectively how well the cylinder is filled with air and fuel.
The design of a valve train determines several parameters that can affect the operation of an engine. Ideally, these parameters could be modified or altered real-time during the operation of the engine to meet the ever-changing requirements of the engine. One of these parameters is valve timing. Valve timing is described as the opening and closing points of valve events as measured in crankshaft degrees. The combination of intake and exhaust valve timing is significant in the way in which an engine performs. Lobe separation angle (LSA), is described as the separation angle (in degrees of camshaft rotation) between the centerline of the intake valve event and the centerline of the exhaust valve event. This parameter has numerous effects on the operation of the engine. The following is a list of some of the effects of varying LSA:
Increasing Lobe Separation Angle
                1. Broadens power band.        2. Decreases peak torque.        3. Reduces maximum cylinder pressure.        4. Decreases the likelihood of detonation.        5. Decreases cranking compression.        6. Idle vacuum is increased.        7. Idle quality is increased.        8. Piston-to-valve clearance is increased.        9. Valve overlap is decreased.Decreasing Lobe Separation Angle (LSA)        1. Narrows power band.        2. Increases peak torque.        3. Increases maximum cylinder pressure.        4. Increases the likelihood of detonation.        5. Increases cranking compression.        6. Idle vacuum is decreased.        7. Idle quality is decreased.        8. Piston to valve clearance is decreased.        9. Valve overlap is increased.        
Optimal valve overlap varies substantially with engine speed and thus being able to change this parameter as engine speed changes would be very beneficial to the overall performance of an engine.